This invention relates generally to a method and apparatus for diagnosing eye conditions or diseases.
There are many disorders that affect the iris, which is the pigmented structure at the front of the eye. One such disorder is pigment dispersion syndrome (PDS), a disorder that is characterized by a mechanical debridement of pigment from the back surface of the iris. As a result of PDS, pigment granules are deposited on structures within the anterior segment of the eye, most importantly the trabecular meshwork (the structure within the eye that permits drainage). Prolonged deposition of pigment granules in this structure may cause a reduction in the ability of the trabecular meshwork to transport fluid from the eye, which can result in an elevation of the intraocular pressure and glaucoma.
Glaucoma is a frequent complication of the condition, with estimates for the progression from PDS to pigmentary glaucoma ranging as high as 50%. Pigmentary glaucoma is now generally considered as one of the more-common forms of secondary glaucoma.
For the eye care practitioner, visual evaluation of the iris using visible-light transillumination is an important and fundamental technique that is used routinely by optometrists and ophthalmologists in their daily practice. However, the value of this technique is severely limited by the low transmission coefficient of the iris and skin for light in the visible regime. For example, PDS is a fairly common condition. Using conventional examination techniques, PDS has been fond in 2.45% of caucasians undergoing glaucoma screening. However, the true prevalence is probably much greater than this because mild presentations go undetected by traditional examination methods. It has been widely assumed that PDS is very rare in black patients; however, recent research has shown that this observation is probably due to the poor sensitivity of standard diagnostic methods, especially for patients having dark eyes and/or skin, which can severely limit visible-light transillumination.
Traditionally, iris evaluation has been performed with the room lights turned off and the patient positioned with his or her head in front of a slit lamp biomicroscope, which is an instrument used to examine the eye visually under magnification. With the patient looking straight ahead, a small beam of light is directed into the eye through the pupil. The practitioner then visually evaluates the front side of the iris for penetration of reflected light from inside the eye. Normally the iris is fairly opaque and reflected light will not be observed. However, the diseased iris may be thinned in some areas due to loss of pigment granules or tissue atrophy, and thus may permit light to penetrate.
In an alternative method, which is typically performed without the aid of a slit lamp biomicroscope, a fiber-optic light source is placed against the lower eyelid and directed toward the globe of the eye. As in the above method, with the room lights off, the practitioner visually examines the front side of the iris for evidence of penetration by internally reflected light. This second method suffers from the same limitations as the first method.
Both of these methods are somewhat useful in routine practice. However, their success is limited by the low contrast of the features that are observed, which is especially problematic for patients with brown eyes and/or dark skin, or in cases when the disease is subtle or in an early stage of progression. In these situations, the reflected visible light may not penetrate the iris tissue even though iris atrophy and/or pigment granule loss is present. Thus, thinned areas may not be appreciated.
Currently, there are no devices available to the clinician for routine imaging or automated detection of iris defects. There is thus a need for a relatively inexpensive and simple device for use in routine clinical use. There is also a need for a device that records the analysis for tracking of disease progression.